Thermodynamic properties of alcohol +alkane mixtures. I. Theoretical results for the hydrogen bond contribution to the excess energies.

Abstract

Using molecular models with the hydrogen bond as the only contributing interaction, the results from existing theories for the excess energies of mixtures with an associating component are compared with each other and with the experimental results for alcohol + alkane systems. After excluding the Redlich-Kister theory as inappropriate, these comparisons are made very effectively using plots of mixture property against composition parameter as then, for each of the Kretschmer-Wiebe or Barker models, one curve gives to a good approximation the mixing property for all systems for any values of the hydrogen bond free energy and enthalpy parameters. The results from the Kretschmer-Wiebe model are essentially the same as those from one of the two Barker models considered.     For a given temperature and alkane solvent the experimental excess free energies can also be approximately summarized by one parent mixture property curve. As shown previously this is also true for the excess enthalpies so that comparison of theory and experiment is made very easy by this approach as the results for individual systems do not have to be considered. The theoretical results are in qualitative agreement with the experimental results but give poor values for the excess energies. As deduced from excess enthalpies the extent of hydrogen bonding as a function of alcohol concentration differs from that deduced by i.r. measurements, as discussed fully in the following paper, but the theoretical results cannot be made to agree with either of these results. Reported results for more complex models also appear to reflect the quantitative failings of the simple models.